1. Field of the Invention
The present invention relates to a method for producing a multilayer molded article formed by laminating a skin material onto at least a part of the surface of a substrate made from a thermoplastic resin.
2. Description of the Prior Art
A multilayer molded article formed by laminating a skin material having a foam layer onto at least a part of the surface of a substrate made from a thermoplastic resin is used widely in various industrial fields including automobile interior parts (for example, door trim and instrument panel) and interior and exterior parts of domestic electrical appliances.
As a conventional method for producing a multilayer molded article described above, a method in which a skin material is adhered or laminated using an adhesive onto a molded article (substrate) which had previously been formed from a thermoplastic resin by various methods such as an injection molding and an injection press molding and a method in which a skin material is supplied between a pair of mold halves and then a molten thermoplastic resin is supplied to be molded into an intended shape while laminating the skin material onto at least a part of the surface of the substrate are known.
However, the former involved a problematically complicated manufacturing process as well as hazards to human health and environment attributable to the solvents contained in adhesives, while the latter undergoes a compression of a foam layer in the skin material, due to a force by which the skin material is pressed strongly against the surface of the mold half when a molten thermoplastic resin supplied to the molds is molded, resulting in a wrinkle on the surface of the skin material of a molded article obtained, especially when producing a product having a recess on the skin material side in the skin laminating part, which leads to a poor appearance, although it is advantageous in that the skin material can be laminated onto the surface of the substrate at the same time with the molding of the substrate.
We made an effort to develop a method for producing a multilayer molded article having a recess on the skin material side in the skin material laminating region while utilizing an advantageous property possessed by an injection molding and an injection press molding which is the ability of laminating a skin material onto the surface of the substrate at the same time with the molding of the substrate without forming a wrinkle on the surface of the skin material, even when a skin material having a foam layer is employed, which leads to a poor appearance, and finally discovered that the relationship between the thickness of the foam layer in the skin material supplied and the minimum radius R of the recess on the skin material laminating side of the substrate in the skin material laminating region of the multilayer molded article is extremely important, thus establishing the present invention.
Thus, the present invention provides a method for producing a multilayer molded article comprising a step of supplying a skin material having at least a foam layer between a pair of a male mold half and a female mold half, supplying a molten thermoplastic resin between the skin material and the molding surface of one of the male mold half and the female mold half, a step of laminating the skin material onto at least a part of the surface of a substrate made from the thermoplastic resin and a step of forming a recess in the skin material laminating region, wherein the thickness, t (mm), of the foam layer in the skin material before molding is 0.6 R or less wherein R represents the minimum radius (mm) of the recess on the skin material laminating side of the substrate in the skin material laminating region of the multilayer molded article.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.